1. Field of the Invention
This invention relates to novel organic compounds and liquid crystal compositions containing the same, and more particularly it relates to organic compounds having an bptically active group and useful as a component of ferroelectric liquid crystal compositions and optically active liquid crystal compositions containing the same.
2. Description of the Related Art
At present, TN (Twisted Nematic) display mode has been most broadly employed, but it is inferior in the aspect of the response rate to emissive display elements such as electroluminescence, plasma display, etc. Thus, various attempts of improvement in this aspect have been made, but it does not appear that a possibility of the improvement to a large extent remains so much.
Thus, various liquid crystal display devices based on a different principle have been attempted, and as one of them, a display method utilizing ferroelectric liquid crystals is proposed (N. A. Clark et al; Applied Phys., lett., 36, 899 (1980)). This mode utilizes ferroelectric chiral smectic C phase (hereinafter abbreviated to SC* phase) or other smectic phases such as SH* phase, SF* phase, SG* phase, etc. and has the following three superior specific features as compared with TN display mode:
a first specific feature consists in that it has a very high response rate amounting to 100 times that of TN display elements; a second specific feature consists in that it has a memory effect so that multiplex drive is easy in combination with the above high rate response properties; and a third specific feature consists in that it is possible to obtain gray scale more easily than TN display mode only by adjusting the inversion time of polarity; hence the mode has been considered to be suitable for graphic display.
However, in spite of such superior specific features, as to currently known ferroelectric liquid crystal compounds and compositions, those satisfying both of the following two conditions have not yet been obtained:
Namely, they have a large spontaneous polarization value required for obtaining the high rate response properties as the first specific feature of ferroelectric liquid crystal compounds as well as a liquid crystal temperature range suitable for practical use. For example, when a compound, ##STR2## as one of compounds disclosed in Japanese patent application No. Sho 61-133269/1986, the invention of which has been made by the present inventors, was added in 20% by weight to a composition exhibiting achiral smectic C phase, the resulting composition exhibited a response rate of 48 .mu.sec at 25.degree. C.; thus it may be said that the compound has approached a stage of practical use. However, reduction in the upper limit temperature of the ferroelectric liquid crystal phase amounted to as high as 20.degree. C. as compared with that prior to the addition of the compound; hence the problem of its practical use has still been left behind. This is because a compound having a large spontaneous polarization value and a preferred mesomorphic range has not yet been found.